Ben Carter
Lighting terminology can be confusing, with terms like lumens, lux, and foot-candles often used interchangeably. However, while they are all units of measurement relating to light, they are not the same thing. Lumens measure the total amount of light emitted from a source, with higher lumens appearing brighter. Foot-candles, on the other hand, measure the amount of light falling on a specific point or object, taking into account factors like distance and beam spread. Lux is the metric equivalent of foot-candles, measuring lumens per square meter instead of per square foot.
| Characteristics | Values |
|---|---|
| Foot-candles definition | Measurement of light intensity |
| Foot-candles unit | fc, lm/ft2, or ft-c |
| Foot-candles usage | Used to measure the number of foot-candles present, which are used to calculate the intensity of motion picture lights |
| Foot-candles vs. lumens | Foot-candles measure the amount of light falling on a specific point or object, while lumens measure the total amount of light emitted from a source |
| Foot-candles and lux | Foot-candles are the imperial measurement, while lux is the metric measurement. 1 foot-candle equals 10.76 lux |
| Foot-candles calculation | Calculation of foot-candles involves determining the size of the area to be illuminated, the height and angle the light will be mounted at, and how much light each fixture will produce |
| Foot-candles and natural light | Foot-candles take natural light loss into account, unlike lumens |
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What You'll Learn
Foot-candles are a measurement of light intensity
Foot-candles (fc, lm/ft2, or ft-c) are a measurement of light intensity. One foot-candle is defined as the amount of light that saturates a one-foot square area with one lumen. Foot-candles are used to measure the amount of light that reaches a surface, rather than the amount of light that leaves a source. For example, a foot-candle would refer to the amount of light on the ground beneath a lamp post, rather than the amount of light the lamp post emits.
Foot-candles are used to ensure that a light source is working properly. Light meters are often used to measure foot-candles, and they are available at many different price points. Most light meters will output their readings in foot-candles or "lux," the SI-derived unit that measures a one-metre square area. One lux is equal to 0.092903 foot-candles.
Foot-candles are especially important for reading light levels in a facility. They indicate how much light is illuminating a specific area, rather than how much light is emitted from a fixture. Foot-candles also account for natural light loss, which lumens do not. When auditing commercial facilities, lighting professionals obtain a foot-candle measurement for each area to ensure that employees are working in safe and productive environments.
Foot-candles are also used in cinematography to calculate the intensity of motion picture lights, allowing cinematographers to set up proper lighting-contrast ratios when filming. Horticulturalists also use foot-candles to measure and discuss optimum light intensity for various plants.
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Lumens are a measure of luminous flux, or flow of light
Lumens are a measure of luminous flux, or the flow of light. The lumen (lm) is the SI unit of luminous flux, which quantifies the perceived power of visible light emitted by a source. Luminous flux is a measure of human visual response, and it differs from radiant flux, which measures the total power of electromagnetic radiation, including non-visible radiation such as infrared and ultraviolet light.
Luminous flux accounts for the sensitivity of the human eye by weighting the power at each wavelength with the luminosity function, which represents the eye's response to different wavelengths. This weighting is standardized by the CIE and ISO. The number of candelas or lumens from a source depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The higher the lumens, the brighter the source will appear. Lumens are the most common measurement you'll see when shopping for LED lighting. The typical luminous efficacy of fluorescent lighting systems is 50-100 lumens per watt.
Luminous flux (in lumens) is a measure of the total amount of light a lamp puts out. It is the rate of flow of luminous energy. A single-foot candle is the amount of light that falls on a surface one foot away from a single candle. One foot-candle is defined as enough light to saturate a one-foot square with one lumen of light.
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Foot-candles are used in cinematography to calculate lighting-contrast ratios
Foot-candles are a measurement of light intensity, or illuminance, that measures the amount of light that reaches a surface area. One foot-candle is defined as one lumen per square foot. In other words, it is the amount of light that falls on a surface one foot away from a single candle.
In cinematography, incident light meters are used to measure the number of foot-candles present. Cinematographers can then use this information to set up the proper lighting-contrast ratios when filming. For example, a cinematographer may use a light meter to determine that a particular scene requires a lighting setup that produces 100 foot-candles.
Foot-candles are also used in other fields, such as horticulture, where light intensity is important for photosynthesis in plants. Similarly, in commercial and industrial facilities, foot-candles are used to ensure appropriate lighting levels for employee safety and efficiency. OSHA (Occupational Safety and Health Administration) has specific foot-candle requirements for certain spaces and industries.
It is important to note that foot-candles are commonly used in parts of the world that follow United States customary units of measurement, such as the US. In other parts of the world, such as Europe, the SI-derived unit "lux" is used. One lux is equal to one lumen per square meter, and a single foot-candle is equivalent to approximately 10 lux.
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Lux is the metric equivalent of a foot-candle
Lumens, lux, and foot-candles are all units of measurement used in lighting terminology. Lumens are a measure of luminous flux, or the flow of light, and measure the amount of visible light emitted from a light source. Foot-candles, on the other hand, measure the amount of light falling on a specific point or object. Lux is the SI-derived metric equivalent of a foot-candle, which is used in places that follow the United States customary units of measurement.
While lumens and foot-candles are not the same thing, they are both relevant measurements in lighting. Lumens measure the output of a light source, whereas foot-candles measure the amount of light that reaches a surface area. For example, a foot-candle relates to the amount of light on the ground beneath a parking lot light, rather than the output of the light itself. Similarly, lux measures the illuminance or amount of light falling on a surface.
In the motion picture cinematography field in the US, incident light meters are used to measure the number of foot-candles present, which are then used to calculate the intensity of motion picture lights. Light meters are also used by lighting professionals to calculate the type of lighting and the lighting needs of a facility. Foot-candles are also important for reading light levels in a facility.
As LED lights have become more common, many users focus on a high lumen output when choosing a light. However, this does not take into account the beam spread or the distance from the desired target point. An LED light with a high lumen output but a narrow beam will not illuminate a large area. Therefore, foot-candles are important when determining the size of the area to be illuminated, the height and angle the light will be mounted at, and how much light each fixture will produce.
To summarise, lux is the metric equivalent of a foot-candle, and both measure the amount of light falling on a surface. Lumens, on the other hand, measure the light output of a source, and are not the same as foot-candles.
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Lumens are the most common measurement when shopping for LED lighting
The definition of a lumen is "a unit of luminous flux in the International System of Units, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions". In short, lumens equal brightness.
With the advent of new, energy-efficient LED technology, we can no longer rely on wattage to indicate how bright a bulb is. Wattage measures energy use, not light output. As a rule, you can replace a standard 75W bulb with an energy-saving bulb of about 1100 lumens. On the low end, replace a 40W bulb with an LED bulb of about 450 lumens.
To help consumers, the Federal Trade Commission requires manufacturers to include a product label for light bulbs on the package. This helps people buy the lightbulbs that are right for them. The Lighting Facts label helps consumers understand what they are purchasing.
Foot-candles are another unit of measurement used to describe light intensity. One foot-candle is defined as enough light to saturate a one-foot square with one lumen of light. Foot-candles are used most commonly in places that follow the United States customary units of measurement. In other parts of the world, the SI-derived measurement "lux" is used.
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Frequently asked questions
A foot candle (fc, lm/ft2, or ft-c) is a measurement of light intensity. One foot-candle is defined as enough light to saturate a one-foot square with one lumen of light.
Lumens (lm) measure visible light from a lamp or light source. The higher the lumens, the “brighter” the source will look.
No, they are not the same thing. Lumens measure the amount of light emitted from a source, while foot candles measure the amount of light falling on a specific point or object.
Foot candles are important for reading light levels in a facility. They show how much light is illuminating an area, taking into account natural light loss, unlike lumens.
Foot candles can be measured using a light meter or design software. Light meters are available from many manufacturers at various price points.
